This invention relates to a safety vent for an internally pressurized fluid container and to a container incorporating the safety vent.
Pressurized fluid containers are well known and widely used for packaging and dispensing a variety of fluid products, including liquids, gases and combinations thereof. These containers perform entirely satisfactorily under normal operating conditions. However, when the contents of such a container become over pressurized by subjecting the container to excessive temperatures, because of improper use or for any other reason, the can will explode and portions of the can may be propelled at dangerously high velocities. Such conditions may occur when the can is accidently subjected to high temperatures during improper use or storage or when the can is incinerated, for example. In order to provide for the safe release of a pressure build-up within the can, a safety vent for the high pressure must be provided. To this end, numerous pressure release devices have been proposed in the art for internally pressurized fluid containers. However, for a variety of reasons including unreliability, high costs, difficulty of maintaining critical tolerances during manufacture, etc., none of these devices have been wholly satisfactory.
One type of known pressure release device for an internally pressurized fluid container is illustrated in FIG. 1 of the drawings. The internally pressurized fluid container 1 shown there is formed with a tubular side wall 2 and upper and lower end walls 3 and 4 which are connected to the tubular side wall. A nozzle or valve 5 is provided in the upper end wall for dispensing the pressurized fluid from the container. The lower end wall or bottom 4 of the container is a dome-shaped inwardly concave end wall which is formed with a single weakened line 6 of reduced material thickness in the form of a score line shaped as an arc of a circle. The end wall has a structural integrity which reacts to an increase in fluid pressure above a prescribed level by initially undergoing at least a partial eversion at a random location along the annular outer area thereof. This eversion or deformation commences then progresses inwardly to stress the weakened line of reduced material thickness and fracture the same whereby the high pressure fluid can be vented from the container.
The aforementioned type of safety vent or pressure release device can be problematical because of the relatively deep scoring which may be required to ensure that venting will occur when the internal pressure of the container exceeds a predetermined level. That is, since the eversion or deformation starts at a random location around the outer periphery of the bottom, the orientation of the weakened line with respect to advancing deformation or eversion is unpredictable. Because the stress experienced at the weakened line during eversion can vary as a function of this orientation, the residual thickness of the material of the end wall at the weakened line must be sufficiently thin to be fractured at the lowest possible stress. The requirement for deep scoring creates manufacturing problems. For example, with a residual material thickness at the weakened line of only 0.0005 to 0.001 inch, there will be a higher number of rejects during manufacturing and a higher number of defective containers referred to as shelf leakers which permit the pressurized fluid to escape from the container, as compared with the numbers of rejects and shelf leakers which occur in scoring material while leaving a greater residual material thickness. Small residual thicknesses at a weakened or scored line can also be problematical in that when the pressurized container is dropped from a shelf, for example, the impact of the container on the floor can fracture the end wall at the weakened line and release the pressurized fluid. If this release is too fast, the container can be propelled in the manner of a rocket and pose a safety hazard to surrounding persons.
Thus, an object of the present invention is to provide an improved safety vent for an internally pressurized fluid container which avoids the aforementioned disadvantages of the known safety vents or pressure release devices. More particularly, an object of the invention is to provide an improved safety vent for an internally pressurized fluid container comprising a wall of the container which is subject to outward deformation when the internal pressure of the container exceeds a predetermined level, with the wall having a weakened line of reduced material thickness formed therein which is adapted to fracture to vent the pressurized fluid from the container in response to the stresses thereon during the outward deformation of the wall, wherein the residual material thickness of the wall at the weakened line need not be extremely small to ensure fracture thereof and venting when the internal pressure exceeds a predetermined level. Thus, manufacturing problems resulting in a high number of rejects or shelf leakers can be avoided.
A further object of the invention is to provide a safety vent for an internally pressurized fluid container of the aforementioned type which has a sufficiently thick residual material thickness at the weakened line that the container can be accidentally dropped without risking fracture of the weakened line of reduced material thickness simply from the impact of the container striking the floor or other surface.
Another object of the invention is to provide an improved safety vent for an internally pressurized container which controls the direction of pressure release to the side of the container to prevent the container from being propelled in the manner of a rocket regardless of the rate of pressure release thereby reducing the safety hazard to surrounding persons.
An additional object is to provide an improved safety vent which opens almost immediately with the initiation of deformation of the container wall and wherein the degree of opening is controlled for safe venting under a wide variety of conditions.
Still another object of the invention is to provide an improved safety vent with a performance which does not depend on the cross-sectional area of the scored area in the container wall but on the whole wall.
These and other objects of the invention are attained by the safety vent for an internally pressurized fluid container of the invention which comprises a wall of the container which is subject to outward deformation when the internal pressure of the container exceeds a predetermined level, a weakened line of reduced material thickness formed in the wall and adapted to fracture to vent the pressurized fluid from the container in response to the stresses during the outward deformation of the wall, and means for controlling the location in the wall at which the deformation starts when the internal pressure of the container exceeds the predetermined level. It has been found that by controlling the location of the initiation of deformation, the orientation of the advancing deformation with respect to the weakened line can be optimized to uniformly create relatively high stress for fracturing the weakened line when internal pressures in the container exceed a predetermined level. Thus, an extremely thin residual material thickness at the weakened line is not required for reliable opening of the safety vent and the operation of the vent is made less dependent upon this thickness.
According to the disclosed form of the invention, the means for controlling the location in the wall at which the deformation starts includes means for locally weakening the resistance of the wall to outward deformation from the internal pressure of the container. The location of the weakened area or areas determines where deformation will be started when the internal pressure of the container exceeds the predetermined level. The degree of weakening can be selected to control the internal pressure at which deformation will start. In this form of the invention the means for controlling the location in the wall at which the deformation starts also controls the direction in which the outward deformation progresses so that its progress is in a direction toward the weakened line of reduced material.
In the preferred form of the invention the container wall containing the safety vent is an end wall which is joined to or formed integrally with one end of a tubular side wall of the container. The weakened line of reduced material thickness is preferably located in a central portion of the end wall. The means for controlling the location in the end wall at which the deformation starts is located radially outwardly from the weakened line and is in the form of an elongated rib formed in the wall and extending in a radial direction in the end wall between the outer rim of the end wall and the weakened line. The rib locally weakens the resistance of the end wall to outward deformation so that deformation is initiated along the outer rim of the end wall at a point spaced radially outwardly from the end of the elongated rib. The deformation progresses radially inwardly from the end of the elongated rib. The rib itself is very strong and resists deformation so that it acts as a lever to transfer stress from its one end adjacent the deformation to its other end adjacent the weakened line. If a small amount of deformation occurs it will result in a small opening or tear at the weakened line for venting while a larger deformation associated with a larger pressure build-up will result in a larger opening or tear. In this way the degree of opening is controlled for safe venting under a wide variety of conditions. The manner of opening of the vent is also such as to result in venting of the pressurized fluid toward the side of the container to preclude rocket-like action. The weakened line of reduced material thickness is located so as to extend transverse to the direction of progressive deformation to facilitate fracturing at the weakened line and venting of the container. In the disclosed form of the invention the weakened line of reduced material thicknesas is in the form of an arc of a circle located in the end wall.
While a single elongated rib and weakened line can be used in a safety vent according to the invention, in the disclosed preferred embodiment of the invention a pair of weakened lines of reduced material thickness in the form of arcs are located in spaced relationship on opposite sides of a circle about the center of the end wall and a pair of elongated ribs are formed in the end wall radially outwardly from central portions of respective ones of the weakened lines with the elongated ribs extending in radial directions in the end wall. The internal pressure of the container at which deformation of the end wall and venting occur can be controlled according to the invention by selection of the rib length, depth and location so that the venting pressure is less dependent on the residual material thickness at the weakened line. As a result, according to the invention, the residual material thickness at the weakened line need not be extremely small or have high tolerances but can be between 0.002 and 0.005 inch, for example. This reduces the manufacturing problems which can occur where residual thickness of only 0.0005 to 0.001 inch are required. The use of higher residual thicknesses at the weakened line also eliminates the problems associated with accidental opening when an internally pressurized fluid container is dropped or otherwise impacted.
These and other objects, features and advantages of the invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for purpose of illustration only, one preferred embodiment in accordance with the invention.